Thread-cutting device for lock stitch sewing machines

ABSTRACT

Thread-cutting device for lock stitch sewing machines having a looper rotating in a horizontal plane, a bobbin housing having an outlet opening for the looper thread which is secured against rotational movements by means of a stop finger below the stitch plate and a thread catcher cooperating with a cutter that rocks in a path of movement disposed perpendicularly to the shaft of the looper, which has a V-shaped incision defining a catcher point having legs disposed in a plane generally parallel to the looper shaft which is movable between the bobbin housing and the retaining finger that extends from the wall surface of the housing laterally and upwardly, where the upper leg of the thread catcher is of greater length than the lower leg, and that the rocking movement of the thread catcher for seizing the threads to be cut is moved by its drive arrangement in a manner that the point of the upper leg first moves between the looper thread outlet opening of the bobbin housing and the retaining finger above the surface of the looper thread outlet opening and upon seizing the looper thread below the surface of the bobbin housing surface.

United States Patent [72] Inventor Kristen Hedegurd Gentolte, Denmark [2]] Appl. No. 62,575

[22] Filed Aug. 10, 1970 [45] Patented Nov. 30, 1971 [73] Assignee Firms G. M. Phil AG.

Kaleerslautern am Pfalz, Germany [32] Priority Aug. 16, 1969 [33] Germany [54] THREAD CUTTING DEVICE FOR LOCK STITCH 3,503,355 3/1979 Hagemeyeretal. 112/252 Primary Examiner-James R. Boler AttorneyRobei't H. Jacob ABSTRACT: Thread-cutting device for lock stitch sewing machines having a looper rotating in a horizontal plane, a bobbin housing having an outlet opening for the looper thread which is secured against rotational movements by means of a stop finger below the stitch plate and a thread catcher cooperating with a cutter that rocks in a path of movement disposed perpendicularly to the shaft of the looper, which has a V-shaped incision defining a catcher point having legs disposed in a plane generally parallel to the looper shaft which is movable between the bobbin housing and the retaining finger that extends from the wall surface of the housing laterally and upwardly, where the upper leg of the thread catcher is of greater length than the lower leg, and that the rocking movement of the thread catcher for seizing the threads to be cut is moved by its drive arrangement in a manner that the point of the upper leg first moves between the looper thread outlet opening of the bobbin housing and the retaining finger above the surface of the looper thread outlet opening and upon seizing the looper thread below the surface of the bobbin housing surface.

PATENTEU "W30 I97| SHEH 10? 2 S'HEEY 2 OF 2 PATENTED NUV30I97| m vew ran m/smvammnm BY THREAD-CUTTING DEVICE FOR LOCK STITCH SEWING MACHINES BACKGROUND OF THE INVENTION The present invention relates to thread cutters for sewing machines. More in particular the invention concerns a threadcutting device for lock stitch sewing machines having a looper that rotates in a horizontal plane, a bobbin housing provided with an outlet opening for the looper thread, which is secured against rotational movements by means of a stop finger and a thread catcher which is rockable along a path of movement perpendicular to the looper shafi.

In a known thread catcher arrangement a thread catcher is provided which rocks about an axis that extends parallel to the looper shaft, whose point has a V-shaped recess. The legs of the thread catcher that move in a plane substantially parallel to the looper shaft are moved between the bobbin housing and the stopping finger that extends laterally and upwardly from the wall surface and during the first part of the movement of the thread catcher seize the needle thread as well as the looper thread. During the further course of the thread catcher movement the two threads seized are located in front of an opening that extends from the intersection of the two legs of the V- shaped recess and are fed to and cut by a cutter that enters this opening. The arrangement of the two legs is such that the upper leg of the thread catcher moves above the plane of the surface of the bobbin housing and the lower leg moves below the plane of the surface of the bobbing housing.

SUMMARY OF THE INVENTION It is an object of the invention to provide a thread-cutting device for lock stitch sewing machines having a looper that turns in a horizontal plane which makes it possible to seize part of the needle thread loop and the looper thread with a single thread catcher and to sever the two threads closely below the bottom of the material being sewn.

In order to accomplish this purpose the invention is based on the technical problem to so seize the looper thread and the needle thread that the part of the needle thread loop going to the material extends laterally of the looper thread to be seized and the cutting location of both threads is displaced from their location of seizure at the thread catcher in the direction of the stitch hole.

In accordance with the invention this problem is solved in that the upper leg of the thread catcher is of a greater length with respect to the lower leg, and the point of the upper leg is movable for seizing the looper thread between its outlet opening from the bobbin housing and the retaining finger above the plane of the looper outlet opening, and afiersein'ng the looper thread below the plane of the bobbin housing surface.

It is possible with this feature in accordance with the invention to first ride over the looper thread with the upper leg of the thread catcher that moves between the looper thread outlet opening of the bobbin housing and its retaining finger above the level of the looper thread outlet opening, i.e., to bring it into engagement at the lower side of the upper leg and then direct the further movement of the thread catcher that extends essentially to the retaining finger to bring it into a position in which the part of the needle thread loop guided over the bobbin housing surface by the looper slides above the upper leg of the thread catcher. Inasmuch as a thread passage space remains between the retaining finger and the lower leg of the thread catcher that is shorter with respect to the upper leg of the thread catcher, the needle thread loop that drops from the bobbin housing to be pulled up by the thread talceup lever is pulled about the upper leg of the thread catcher, while during the following pulling movement of the thread takeup lever the part of the needle thread loop leading to the thread supply extends along the upper side of the thread catcher, while the part of the needle thread loop leading to the material extends from the intersection of the two legs of the thread catcher closely along and parallel to the looper thread at the side surface of the thread catcher that faces the needle. If the two threads are severed in the area of the stitch hole of the stitch plate, then the thread ends remaining on the material become optimally short because they extend from the cutting location to the stitch hole while the threads remaining with the thread supply are optimally long because they extend from their cutting location to the intersection of the two legs of the thread catcher and only from there to the thread supply, i.e., to the looper thread outlet opening respectively through the stitch hole to the needle.

A simple solution from the standpoint of structure for displacing the stitch location of both threads from the intersection of the two legs of the thread catcher to the cutting hole, which at the same time affords a maximum measure of operating security for accurately located cutting of these threads, results from a recess on the side of the thread catcher facing the needle from the intersection of the two legs and parallel to its path of movement, the terminal edge of which defines a countercutter for the cutter.

To displace the path of movement of the upper leg of the thread catcher from its first path of movement above the looper thread outlet opening to the second path of movement below the level of the bobbin housing surface, the thread catcher has a curved cam groove in its wall in accordance with a further development of the invention, into which a supporting roller extends that is disposed essentially perpendicularly to its axis of rocking.

The invention will be described more in detail with reference to an embodiment illustrated in the accompanying drawings, in which FIG. I is an overall view of the sewing machine from the front,

FIG. 2 is a perspective illustration of the thread catcher and its drive after the cutting operation is completed,

FIG. 3 is a perspective view of the thread catcher after seizing the looper thread,

FIG. 4 is a section along line IV-IV in FIG. 3,

FIG. 5 is an enlarged illustration of the thread catcher upon seizing the needle thread,

FIG. 6 is a side view of the thread catcher shortly before the cutting of the two threads.

DESCRIPTION OF THE INVENTION The standard 2 is mounted upon the baseplate l of the sewing machine (FIG. 1) with the horizontal arm 3 formed thereon that ends in the head 4. The arm shaft is joumaled in the arm and is in operative connection with the needle bar 7 carrying the thread guiding needle 6 that moves up and down. In the head 4 of the sewing machine there is furthermore journaled, in a known manner, the thread take up lever 8 that effects a reciprocating movement, which is likewise driven by the arm shaft 5. On the arm shaft 5 a belt wheel 9 is mounted which transmits the drive movement by way of belt 10 and a counter wheel 11 to the arm shaft 5 and to the looper drive shaft 12 joumaled in the baseplate 1. Upon the looper drive shaft 12 a pinion 13 is secured which meshes with a counter wheel 15 disposed upon the vertical looper shaft 14 and thus drives the lock stitch looper 16 that rotates in a horizontal plane and is fastened to the upper end of the looper shaft 14.

The lock stitch looper I6 (FIG. 4) has a looper body I7 and a looper point 18. In the lock stitch looper a bobbin housing 19 is joumaled which at its wall surface facing the needle supports a retaining finger 20 that extends laterally and upwardly. The bobbin housing retaining finger 20 extends into a recess 22 of the stitch plate 21 provided at the lower side of the base plate I and thus secures the bobbin housing I9 against rotary movement. In the bobbin housing 19 the looper thread is arranged in a known manner upon the bobbin (not illustrated) which is brought out of the bobbin housing through an outlet opening 23 provided in the bobbin housing at the upper side thereof.

Laterally of the looper shaft 14 a thread catcher 25 is arranged that is mounted on a shaft 24 essentially parallel thereto which rocks closely above the bobbin housing 19. The point of the thread catcher 25 is disposed angularly vertically downwardly as reflected particularly by FIGS. 3 and 5 and is provided with an essentially V-shaped recess. Both legs 26, 27 of the thread catcher 25 that are formed by the V-shaped recess are movable along a path of movement extending between the bobbin housing 19 and the retaining finger 20 that extends laterally and upwardly from its wall surface. As shown particularly by FIG. 5, the leg 26 that is rounded and directed downwardly is of a greater length above the lower leg 27 for a purpose to be explained later. At the lateral surface of the thread catcher that faces the needle, a recess 28 is provided that extends from the intersection of the two legs 26, 27 and parallel to the path of movement of the thread catcher and ends in a bore 29. The terminal edge of the recess or the limiting edge of this bore 29 defines a counter cutter 30 for a cutter 3] that cooperates with the thread catcher 25. It is received by a support 32 mounted at the bottom of the base plate 1 upon which a thread clamp 33 is arranged that is formed in a known manner. lt will be explained later how the two legs 26, 27 move between the cutter 31 and the thread clamp 33.

Below the thread catcher a ring 34 is mounted on the rocking shaft 24 thereof which has a wall curve groove formed in a manner shown in FIG. 2 into which a supporting roller 36 extends that is disposed perpendicularly to the rocking shaft 24 and which is likewise adjustably secured to the support 32. At its lower end the rocking shaft 24 has a crank 37 whose free end is pivotally connected with a drawbar 38. A double lever 39 is joumaled on the free end of this drawbar 38, which is linked at one end by means of a pin 40 to a bifurcated head 41 and at the other end by means of a pin 42 to a bifurcated head 43. The drawbar of an electromagnet 44 is connected with the bifurcated head 41 and the magnet is secured to the bottom of the baseplate l by means of a support 45. Between the support 45 and a setting ring 46 provided on the bifurcated head 41, a spring 47 is arranged which serves in a manner to be explained hereinafter for returning the thread catcher 25 to its initial position. With the bifurcated head 43 the drawbar of a second electromagnet 48 is connected which is likewise secured to the bottom of the baseplate l by means of a support 49. Between this support 49 and a setting ring 50 provided upon the bifurcated head, a pressure spring 51 is mounted which likewise serves for guiding the thread catcher 25 back to its starting position.

The manner of operation of the thread cutting device is as follows:

At the end of the seam the machine with the needle in a predetermined position, for example in the low position, is briefly stopped by a stop matikmotor and simultaneously the circuit of the electromagnet 48 is closed. The magnet 48 pulls up and thereby rocks the double lever 39 about the pin 40 which no serves as pivot for the bifurcated head 41. As a result, the thread catcher 25 effects a clockwise rotary movement whereby its upper leg 26 moves above the looper thread extending along a path of movement leading between the wall surface of the bobbin housing 19 and its retaining finger 20. The looper thread outlet opening 23 to the stitch hole bottom of the leg 26 thus engages the looper thread in a manner shown in FIG. 3. During the further course of the movement of the thread catcher 25, the same is moved so far that the point of the upper leg 26 is located in the proximity of the retaining finger 20. Thus the thread catcher 25 is moved simultaneously downwardly in accordance with the shape of the wall cam groove 35, whereby the point of the upper leg 26 is moved downwardly so far from its first path of movement above the level of the looper thread outlet opening 23 until it is located below the level of the bobbin housing surface.

During this first phase of movement of the thread catcher, the needle 6 has again stitched and the looper point 18 has seized the needle thread loop. During the guiding of the needle thread loop around the bobbin housing 19, the part of the needle thread loop guided by the looper thread point over the top side of the bobbin housing 19 slides over the upper leg 26 of the thread catcher. After the needle thread loop starts to drop from the looper 16, the thread takeup lever begins its upward movement in a known manner and with the needle tension open draws the needle thread loop disposed about the upper leg 26 of the thread catcher between the retaining finger 20 and the lower leg 27 that is shorter with respect to the upper leg 26 onto the upper leg 26 of the thread catcher 25. The part of the needle thread loop going to the thread supply is located in this connection on the top side of the leg 26, while the part of the needle thread loop going to the material together with the looper thread rests against the lower side of the leg 26. After the thread take up lover 8 has reached the proximity of its upper dead point, the electromagnet 44 is put under tension and swings the double lever 39 over its bifurcated head 4! about the pin 42 which now serves as pivot. The thread catcher 25 is thus moved along in the same direction as during its first movement and pulls the looper, as well as the needle thread supply along as the needle thread tension is still open. The parts leading to the material from the needle and the looper thread come to rest during this movement in the recess 28 that extend from the intersection of the two legs 26, 27 of the thread catcher 25 while the part of the looper thread leading to the looper thread supply extends from the intersection of the two legs 26, 27 to the looper outlet opening 23 and the part of the needle thread leading to the thread supply leads by way of the thread catcher 25 to the needle thread supply. At the end of the pull out movement of the thread catcher 25 the part of the looper thread leading to the looper thread supply is guided and clamped in the thread clamp 23 laterally between the two legs 26, 27 while the parts leading to the material from the needle and looper thread resting in the recess 28 are severed at the outlet edge of the recess by the cutter 3l resting against the side wall of the thread catcher facing the needle. After the thread catcher 25 has reached its final position the current circuit of both magnets 44, 48 is opened the two springs 46, 51 now relaxing lead the thread catcher again into its initial position.

The ends of the needle and looper thread remaining on the material become optimally short because the cutting of both threads takes place at the terminal edge 30 of the recess 28 located at the side surface of the thread catcher facing the needle and these threads extend from their cutting location directly to the sewing material, while the ends remaining on the individual thread supplies, since they extend from the cutting location to the cutting point of the two legs 26, 27, i.e. to their seizing location and only thence to the thread supply, are given a length that insures the forming of the initial stitches of the next following sewing cycle.

Having now described the invention with reference to the embodiments illustrated in the drawings what it is desired to claim as applicants invention is set forth in the appended claims.

I claim:

1. Thread-cutting device for lock stitch sewing machine of the type having a looper supported on a vertical looper shaft and rotating in a horizontal plane and a needle adjacent to and movable relative to said looper, comprising a bobbin housing having an outlet opening for the looper thread, a retaining finger extending laterally of and upwardly from the wall surface of said housing to secure said housing against turning, a thread catcher mounted on a catcher shaft generally parallel to said vertical shaft and movable in a horizontal plane, a cutter disposed along the path of movement of said catcher, said catcher having a catcher point provided with a V-shaped recess with legs disposed above one another parallel to said looper shaft and being movable between said bobbin housing and said retaining finger, the upper leg of said catcher having a point and being of greater length than the lower leg, operating means for imparting a rocking movement to said catcher to move said point of said upper leg between said looper thread outlet opening and said retaining finger above the level of said outlet opening and upon seizing the looper thread to move 3. Thread-cutting device in accordance with claim 1, where a cam groove is disposed circumferentially of said catcher shaft and a support is mounted proximate said shaft having a roller extending perpendicularly from said support into said cam groove. 

1. Thread-cutting device for lock stitch sewing machine of the type having a looper supported on a vertical looper shaft and rotating in a horizontal plane and a needle adjacent to and movable relative to said looper, comprising a bobbin housing having an outlet opening for the looper thread, a retaining finger extending laterally of and upwardly from the wall surface of said housing to secure said housing against turning, a thread catcher mounted on a catcher shaft generally parallel to said vertical shaft and movable in a horizontal plane, a cutter disposed along the path of movement of said catcher, said catcher having a catcher point provided with a V-shaped recess with legs disposed above one another parallel to said looper shaft and being movable between said bobbin housing and said retaining finger, the upper leg of said catcher having a point and being of greater length than the lower leg, operating means for imparting a rocking movement to said catcher to move said point of said upper leg between said looper thread outlet opening and said retaining finger above the level of said outlet opening and upon seizing the looper thread to move said point below the level of the surface of said bobbin housing.
 2. Thread-cutting device in accordance with claim 1, where said thread catcher has a groove extending from the intersection of said legs and parallel to the path of movement of said thread catcher, said groove terminating in an edge defining a counter edge for said cutter.
 3. Thread-cutting device in accordance with claim 1, where a cam groove is disposed circumferentially of said catcher shaft and a support is mounted proximate said shaft having a roller extending perpendicularly from said support into said cam groove. 